1. Field of the Invention
The present invention relates to a benzopyran compound, which is an important intermediate in synthesis of optically active pyranobenzoxadiazole compounds useful for the treatment of hypertension, asthma, etc., and to a process for producing the same.
2. Description of the Prior Art
Pyranobenzoxadiazole compounds of the formula [VII]: ##STR4## wherein A represents a hydroxyl group or OC(O)CH.sub.3-n X.sub.n, in which X is fluorine atom, chlorine atom, bromine atom, methyl group or methoxy group and n is 0 or an integer of 1 to 3;
when R.sup.a represents a hydrogen atom, R.sup.b represents a hydrogen atom, C(Z)CH.sub.3-n X.sub.n or C(Z)NHCH.sub.3-n X.sub.n in which Z represents oxygen atom or sulfur atom and n has the same meaning as defined above; and
when R.sup.a does not represent a hydrogen atom, R.sup.a and R.sup.b together form (CH.sub.2).sub.m-1 C(Z) in which m is an integer of 4 or 5 and Z has the same meaning as defined above, (CH.sub.2).sub.m-2 NHC(Z) or (CH.sub.2).sub.m-2 OC(Z) in which Z and m have the same meanings as defined above, are described in Japanese Patent Laid-Open No. Hei 2-49788 (49788/1990), EP-A-0 327 127 and U.S. Pat. No. 4,900,752. The compounds exert intense vasodilatory and hypotensive activities, and thus are expected to be useful as a medicine for treating hypertension, angina pectoris, arrhythmia, cerebral circulation disorder and asthma.
There are two kinds of optical isomers for the compounds of the formula [VII] since the compounds have asymmetric carbon atoms at the 3- and 4-positions of the pyran ring, and only one antipode exhibits excellent activity as a medicine, as shown in Japanese Patent Laid-Open No. Hei 3-141286 (141286/1991), EP-A-0 409 165 and U.S. Pat. No. 5,097,037. However, since the antipode is synthesized from an optically active compound [VIII] (an optically active compound showing dextrorotation in ethanol) as a raw material in accordance with Scheme 1. The production thereof has shown economical problems. (see Japanese Patent Laid-Open No. Hei 3-141286, EP-A-0 409 165 and U.S. Pat. No. 5,097,037) ##STR5##